The economic downturn and a drop in cross-border trading may force tolls on Route Three to rise by one-third next year.

Gary Luk Kam-hon, general manager of Route Three, issued the warning as the 10km country park section of the expressway, which includes the 3.8km Tai Lam Tunnel, marked its first anniversary of operation.

Each day, more than 38,000 vehicles on average use the $7.25 billion Route Three, which links the Ting Kau Bridge and Yuen Long, an increase of about 60 per cent from when it opened.

But the figure is way below the daily projection of 60,000 vehicles made before the economic downturn, said operator Route Three (CPS) Company.

'The economic downturn in Hong Kong and fall in mainland export and import trading as a result of the Asian financial turmoil are the main reasons behind the discrepancies,' Mr Luk said.

In addition, the predicted increase in the flow of cross-border traffic never materialised, he said.

The operator said that as a result, the toll expressway was expected to be tens of millions of dollars off its minimum net income level as set by the authorities each year.

'To recover the deficit, there is a strong possibility that we may have to apply for a toll increase with the authorities once our accountants have returned more complete figures,' Mr Luk said.

If the move is approved, tolls for cars and taxis would rise from $5 to $20, starting from New Year's Day at the earliest, with vans, lorries and trucks having to pay $10 more for the use of the route.

The tunnel is offering a special $10 toll to cars, taxis and all goods vehicles for three days from Friday.